The Controversy Behind the IQ Test

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A popular topic these days, though maybe not as popular as when I was younger, is the concept of the IQ test, which is designed to measure your intelligence quotient. An intelligence quotient (IQ) is a total score derived from a set of standardized tests or subtests designed to assess human intelligence. According to Wikipedia:

“Historically, IQ was a score obtained by dividing a person’s mental age score, obtained by administering an intelligence test, by the person’s chronological age, both expressed in terms of years and months. The resulting fraction is multiplied by 100 to obtain the IQ score. For modern IQ tests, the average raw score  is defined as IQ 100 and scores each standard deviation up or down are defined as 15 IQ points greater or less. As such, around two-thirds of the population scores [are supposedly] between IQ 85 and IQ 115.”

Now, I put an extra emphasis on supposedly above. You can probably take a guess as so why I did this, and if you guessed that it has to do with differential scoring among ethnic and racial groups then you would be correct. That brings into question: why do some groups of people have higher average scores on IQ tests than others?

Despite coming into being over a century ago, IQ tests are still widely used today to measure an individual’s mental ability. In America, these tests show significant differences in scores (lower) when it comes to demographics of different racial and ethnic backgrounds other than white. According to Daniel Murdock, there are two potential reasons for this. 

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Firstly, there is a possible genetic factor that could impact intelligence testing. Most researchers believe there is a reaction range to IQ, in which heredity places an upper and lower limit on the IQ that can be cultivated. This has been found through family studies, that show that intelligence is highly correlated among members in immediate family. Further supporting studies are twin studies that show that intelligence is more highly correlated among monozygotic twins than dizygotic twins. Interestingly enough, adoption studies that show that the IQ scores of adopted children somewhat resemble those of their biological parents, giving weight to the biological/hereditary perspective.

There’s also an environmental perspective to consider. While studies have supported genetic factors, we can’t do away with how the environment can play a part in the development of intelligence. To this end, we must understand the concept of epigenetics. Epigenetics is “the study of the process by which genetic information is translated into the substance and behavior of an organism: specifically, the study of the way in which the expression of heritable traits is modified by environmental influences or other mechanisms without a change to the DNA sequence” according to Simply put, epigenetics is the study of how the environment manipulates the expression of genes without actually causing structural changes to the genes.

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To that end, we must find support for the influence of the environment on IQ – family and adoption studies. Adoption studies provide evidence that our upbringing plays an important role in our mental ability – adopted children show some resemblance to their adoptive parents in IQ. Family studies also show that siblings who are reared together are more similar in IQ than siblings reared apart.

Similarly, when children are removed from deprived environments and placed in homes that are more conducive for learning, they show increases in IQ. While all this so far works on a more individual basis, it serves to set the stage for the big picture: groups.

What in the environment could cause these patterns and changes in IQ? Socioeconomic Status, Health, and Nutrition, and Education. This is true on an individual level as well as it is on a group level. The quotation below was pulled directly from the source as I personally couldn’t find a better and more concise way of putting across what the author said:

  • “Socioeconomic environment: Racial and ethnic minority children are more likely to experience socioeconomic disadvantages, which are correlated with lower IQ scores.” (Group Differences in Intelligence Test Scores, 2018)
  • “Health and nutrition: Racial and ethnic minority children are statistically more likely to be exposed to poorer nutrition, prenatal health care, and postnatal health care. Poor health and nutrition can negatively affect cognitive development and functioning.” (Group Differences in Intelligence Test Scores, 2018)
  • “Education: Racial and ethnic minority children are more likely to be exposed to poorer quality schools than white children, which limits opportunities for cognitive development.” (Group Differences in Intelligence Test Scores, 2018)

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Inspired by the Week 12 SHT topic, this blog post is meant to help me properly articulate my thoughts within the topic of systemic racism and its consequences on the population. However, there is no room here for politics so I’ll leave it at this: the ethnic and racial differences in IQ scoring have nothing to do with biological or genetic limitations specific to one or more racial or ethnic groups. These scores are a product of the environment, the system under which they live and experience.


Group Differences in Intelligence Test Scores. (2018, February 1). Retrieved from